1. Field of the Invention
The present invention concerns a device for radiation therapy implemented with image monitoring.
2. Description of the Prior Art
In the framework of radiation therapy, in general a target within the human body should be irradiated in order to combat illnesses, in particular cancer. A high radiation dose is generated specifically in an exposure center (isocenter) of an exposure device. In order to minimize the radiation dose outside of the target volume and thus to protect healthy tissue, the entire radiation generator is normally moved around the static patient. The radiation dose is thereby concentrated in the beam in the region of the rotation axis.
However, in the exposure the problem frequently arises that the target of the exposure in the body is mobile. For example, a tumor in the abdominal region shifts during the breathing cycle. Moreover, a tumor can also shift, grow or already shrink in the time period between the exposure planning and the actual exposure. It is therefore known to monitor the position of the exposure target in the body during the exposure by imaging in order to be able to appropriately control the beam, or possibly to be able to terminate the exposure, and thus to increase the success of the therapy.
For this purpose, combinations of exposure devices with x-ray-based imaging have been proposed. These known combinations have the disadvantage that the image quality of x-ray-based imaging techniques is not optimal for the depiction of soft tissue (for example tumors), and that monitoring cannot occur simultaneously with the actual exposure (known as “in-line monitoring”) due to interactions between x-rays of the imaging device and therapeutic beams of the exposure device. An example of such a combination is described in U.S. Pat. No. 6,487,274 B2.
Furthermore, combinations of exposure devices with MRI apparatuses (MRI: magnetic resonance imaging) have been proposed to enable an “in-line monitoring”. Compared to combinations with x-ray-based imaging, such combinations offer the advantage that the imaging is less distorted by the exposure and a higher image quality is achieved.
For example, a radiation therapy apparatus with a system for magnetic resonance imaging (MRI system) in which a linear accelerator can be rotated around various axes is known in U.S. Pat. No. 6,198,957 B1. Depending on the selection of the rotation axes, however, parts of the MRI system also lie in the beam path of the radiation therapy apparatus and can thereby scatter and/or attenuate the beam.
United States Patent Application Publication No. 2005/0197564 A1 and WO 03/008986 A2 disclose respective systems for MRI-directed radiation therapy, wherein a radiation therapy unit is arranged between two parts of a bipartite magnet of an MRI apparatus so that the radiation therapy unit can be rotated around a center of the static, divided magnet. Such bipartite magnets are large, expensive and normally achieve a homogeneous magnetic field only in a small volume.
Therefore, a need continues to exist for devices for radiation therapy with image monitoring.